1. Field of the Invention
The present invention relates to a process for producing potassium hexatitanate fibers or composite fibers having excellent heat resistance, heat-insulating property, chemical resistance and reinforcing property.
2. Description of the Prior Art
Heretofore, fibrous potassium hexatitanate K.sub.2 Ti.sub.6 O.sub.13 has been known as a heat resistant heat-insulating material. For the production of potassium hexatitanate fibers, there have been proposed:
(1) a method wherein by means of a flux, a primary phase of potassium tetratitanate fibers is grown in a molten material, followed by treatment for partial removal of potassium and heat treatment to obtain potassium hexatitanate fibers; PA1 (2) a method wherein without using any flux, a mixture of potassium tetratitanate fibers and potassium dititanate fibers is formed as the primary phase by utilizing the incongruent melting-and-association reaction of potassium tetratitanate, followed by treatment for partial removal of potassium and heat treatment to obtain potassium hexatitanate fibers; and PA1 (3) a method wherein potassium dititanate fibers are grown by utilizing the congruent melting of low melting point potassium dititanate, followed by treatment for partial removal of potassium and heat treatment to obtain potassium hexatitanate fibers.
However, in each of these methods, titanium dioxide used as the starting material is a highly pure product at a level of at least 99% produced by treating ilmenite by a sulfuric acid method or chlorine method. Accordingly, the cost for the starting material is high, and it adds to the cost of the final product.